text:
Is it possible for Mig 21 at corner speed to extend the flaps to minimize the turn radius? Or this is not an option?
The corner speed is around 330knots if you want to turn better than the enemy is possible to lower the flaps?

What "other one"? Are you asking about lowering the flaps at 330 knots? Dog fights are about energy management, you don't want to be in a low energy situation.

@RonBeyer Tell that to all the "Cobra" manoeuver advocates :D

I do not know for sure, but I think that using flaps on high sweep wing like that of Mig 21 during a high g maneuver to increase turn rate would not work. Furthermore, I do not think it works very well on any wing type. Leading edge devices are a different story... We must summon @PeterKämpf to rule on this.

@DeepSpace It's mostly an airshow maneuver, its usefulness in combat is questionable with modern generation fighters, specifically because it puts you in a low-energy state and vulnerable to a secondary attacker, or allows the other aircraft to get away.

Jpe61 The F18 trailing edge flaps automatically drop down if hard speed turns7.5G's (corner speed)is executed along side with the Leading edge flaps

It kinds of depends on which version you are asking. Some late versions like Chinese J-7E(also serving Pakistani Airforce as J-7PG) actually has this capability.

Not really.
First, the 'legal' reason: the flight manual doesn't offer this method. So you are not supposed to do it.
Second, there is a technical reason: MiG-21 had so called 'floating flaps' (as they call it), which are held down only by hydraulic pressure. The pressure is set such that the air dynamic pressure would retract the flaps as the airspeed rises above certain point even if the pilot forgot to do it, preventing their damage. I can't find the official threshold, but from memory the flaps would fully (or almost fully) retract at 600 km/h. This is a bit more than 330 kt, but anyway this leaves only marginal available extension at the optimum speed. (Full extension limit was around 340 km/h, but we are not talking about full extension in any case).
Now, what if we did it anyway? Floating flaps make calculations uncertain, but we only need to know if flaps would improve things. For that, we need to know if the turn1 is limited purely by the available lift or by something else. This 'someting else' could be thrust, structural load limits or available elevator deflection.
For MiG-21 (and most fighters), elevator becomes limiting only at supersonic speeds, and structural limits at high subsonic speeds (above the optimum turn speeds).
Thrust is important: we can be pretty sure that flaps will increase drag more than they will maximum lift.
Now, I don't want to post a graph for every statement I make, but all the data is taken from the official flight manual for MiG-21bis (the latest major modification of the fighter). I believe it can be easily found in English, at least for the export versions.
At low altitudes, where the turn radius is actually minimal, the data shows that the available load factor significantly increases with thrust (e.g. 2.5G at max military power vs 3.5G full afterburner at M=0.5,2 which is approx. 330 kt), and the turn radius decreases (~1200 m vs 800 m in the same conditions). This confirms that it is thrust that actually limits (the steady state) performance. Thus, flaps will not help. This is a rather typical situation.
However, turn radius keeps decreasing at lower speeds. (At low altitudes. At higher altitudes, it has a minimum at M=0.5 or more). The official data starts at M=0.5, but if I extrapolate a bit, the speed at which it stops being thrust-limited seems to be quite low. There is a chance that we'll get an optimum somewhere between M 0.3 and 0.4, but it will be a very low-energy turn.
Arguably, if we want to out-turn an enemy, we need the maximum turn rate (= minimum turn time), rather than the minimum radius. This optimum is at much higher speeds (around M=0.8-0.9)3, and there it is also mostly thrust-limited. There is no talk of flaps at such speeds anyway.

1 Of course, we are talking about steady turn. If you just want to turn around the quickest way, you are better off doing a chandelle, an unsteady maoeuvre.
2 At H=1 km (3000 ft), weight 7500 kg (fairly low but reasonable), with two missiles.
3 But this optimum is quite shallow, with little difference in the range M=0.6-0.9 at low altitudes. At higher altitudes, the optimum shifts clearly towards M=0.9. But all this only with full afterburner.

Zeus The 330 knots is about 611kilometers


text:
Does the F-4 Phantom use (have) differential horizontal tail deflection?
Is differential horizontal tail deflection used to roll the aircraft around the longitudinal axis along with the ailerons / spoilers and a bit of rudder?

No, the two sides of the Stabilator are connected to one another and move in unison.
The following is from the USAF F-4E flight manual, page 1-21.

Can you support this? I think you are correct, based on what I know about Phantoms, but on an SE site we prefer supported answers.  Thanks in advance.

(Charles Bretana's answer provides direct evidence.  This answer adds historical context.)
Other fighters use differential elevator to cause roll, F/A-18, F-100, F-15, but not F-4:

F-4 pilots were trained to use the rudder to roll the aircraft at higher AOA. Instructors were trained to emphasize this flight characteristic, and, whenever at high AOA, to keep our knees in the back seat right up against the control stick to inhibit new pilots from introducing any aileron.

R. Kogler's
Automatic limiters in air force aircraft flight control systems confirms that

...pilots originally trained in aircraft like the F-4 were taught to roll at high AOA with rudder commands rather than lateral stick commands to avoid departures [from controlled flight] due to adverse yaw from ailerons and differential tails.

No. The only movement I saw out of the tail when crews checked controls was both sides in unison,for rolling will definitely use rudder at higher AOA.

The rudder movement may be commanded by pilot via pedals.

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text:
What is the problem if the temperature of the oil and heads of cylinders is too high?
What is the problem if the temperature of the  oil and heads of cylinders is too high? What's the fault in piston engines?

Had anyone mention kaboommm!!!!?!

Engines contain explosions. Metal gets weak when too hot. End result?

Your edit changed the meaning of your question, invalidating the (good) answers you received. As originally stated, the question seemed to ask about the bad effects of high temperatures; now it asks about causes.  Might be best to revert your edit & ask a new question about causes.

Piston engines are designed to run within specific temperature ranges. Going above this range might effect the lubrication [hot oil may not provide the right amount of protection to moving parts, If hot enough it could melt seals, or even catch fire.]
the other danger is as metal changes temperature its structural property's change. If a metal gets too hot it becomes softer and may become less resistance to forces. also there is the issue of shock cooling, if a hot engine gets cooled to quickly, it may unevenly cool, and due to the difference in heat expansion could crack or fail.

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text:
Ailerons deflection of the F16 in take off and landing gain?
Let's say you are at a safe altitude and landing gear is down and the aircraft is in To/L gains and you want to do aileron roll and apply full  left (or right ) stick to do the rolling maneuver.The F16 doesn't have any ailerons only flaps moving up and down  .But because is in the  take off /landing gain's with the flaps deployed at maximum angle only one moves other stand still at 20 degrees down .Will the raised flaperon go above the wing cord or not , meaning will  rise up above the cord line of that wing or not passing the wing line ?

As per flight control diagram from General Electric 1975:
The aileron control can command +/-21.5 degs.
The flap control can command +21.5 degs down (even though the HUD will say 20 but there is in this control a +1.5 electrical bias which will be neutralized by the mechanical bias). This is added to the aileron control output.
Then one should subtract the 1.5 degs mechanical flaperon bias.
The flaperons can move +20 to -23. (remember negative is up)
So one flaperon will be at +20 down while the other will be at -1.5 up above the cord given that the aileron produces max aileron roll.
So the question is will the aileron control command max deflection if you are airborne? Most likely no when the aircraft starts rolling, as when the gear is commanded down, internally in the roll system the command will be decreased due to roll rate, and the command is only about half with gears down.
But when you are weight on wheels and the roll rate is zero, you will get one of them 1.5 degs above the cord line, when you command max roll.
Source document: Diagram in AD-A055-417.

So if the F-16 is airborne, with the flaps down and pilot comanded full max roll, the flaperons gives half of max rolling rate(possibly the halfway travel of the flaperons(this is 10degrees under the cord line for the rise up one but this is influenced by the speed at the moment) and when weight is on main wheels then only oneflap will go up 1.5above the cord line. This is my understanding. It is ok?

I made a mistake in my answer, I will update in a while.

Contrary to the first answer, the flaperon will actually go up according to the control surface mixer from the DFLCS control block diagram in DTIC ADA 189675:

Take both the aileron deflection and TEF at maximum deflection, then you will get one flaperon at 21.93, and another at -21.5.


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What is a G-Check and what are the differences relative to other checks?
Tried looking for a definition on wikipedia for a G-Check. The wikipage only mentions A,B,C,D checks.
Any ideas what a G-check exactly is? I think I found an article stating it is a 7500 hr major inspection. What is considered a major inspection relative to a minor?

@SMSvonderTann I'm not sure what to think of forcefully cutting a users question, that seems... wrong. Saying something in the comments is one thing, but removing parts of the question on their behalf? I don't know. I would never do something like this over on SO (where I have enough rep (>20k) to do it).

Can you give an example of where you saw the term "g-check"? Some context might help

Could it be an overweight/high-G landing check? Would be done after any overly forceful landing.

It's tough to tell based on your question, but I think you are talking about an inspection due to an over-G reported on a flight either by the pilot or the flight control system post-flight report.
Maintainers will do inspections of known stress points on the aircraft to look for breaks, cracking or loosened parts and then declare it safe for flight or fix anything out of tolerance.  For a low level over-G, this could be pulling a few panels.  For higher level over-Gs it could be 8 hours worth of work

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text:
What are these five indicators at the front of the 737 passenger cabin?
As a passenger I noticed a set of five indicators on the ceiling at the front of the 737 passenger cabin. They are red, yellow (or white), blue, white, red.

The red ones seem to be coupled together (which could indicate their higher importance and also prevents problem with a failed light bulb).

On the photo, there seems to be two white indicators but on older models I almost certainly remember that one of them was yellow.

I have seen those indicators in old and new 737 models. I understand they inform the cabin crew of something but I did not find any explanation so far.

What is the exact purpose of each indicator?

Are they controlled manually or automatically?

Are they Boeing-specific?

How are similar conditions communicated to cabin crew in other similar types of aircraft (e.g. A320) which do not seem to have these indicators?

@mins – good to see someone has described similar set of lights on Airbus. This set seems to be somewhat different. It has no green light (see the answer there) and it has white and yellow/amber light (or two white lights).

This is the forward Master Call Light Panel installed in the ceiling of the cabin. A second one is located aft. These panels exist on all large aircraft for the cabin crew members to be alerted without staying at their seats.
The number and color of lights vary according to customer requested options for the cabin. Some lights may be duplicated to indicate which side of the cabin is affected (e.g. for the passenger call). These panels are not required by regulation, it's to facilitate the work of cabin crew members.
For the B737
The non customized panel of a B737 looks like this:

Source: Boeing 737 FAM
The lights illuminates and chimes are played:

Pink, HI-LO chime: A crew member dialed the forward station number on the cabin interphone handset.
Blue, HI chime: A passenger pressed the ATTENDANT CALL switch on the Passenger Service Unit.
Amber, HI chime: A passenger in the lavatory pressed the ATTENDANT CALL button.

The white portions are not used, there is no light here.
Source: Boeing 737 NG Flight Attendant Manual (D6-27370-6/7/8/900-FAM).

For the B787

Green, HI-LO chime: Cabin crew call.
Green flashing, HI-LO chime three times: All call.
Pink, HI-LO chime: Flight deck call.
Blue, HI chime: Passenger call.
Amber, HI chime: Lavatory call.
Amber flashing, HI-LO continuous chime: Lavatory smoke.
Amber flashing, HI continuous chime: Crew rest smoke.
Red: Sterile flight deck (pilots mustn't be disturbed except for safety matters, and attendants must expedite operational activities leaving commercial activities for later).

Source

No doubt in a few years, attendants will receive these indications directly on individual portable devices with more details.
Airbus has its own similar colors and chimes, see:

What does a blue light by the toilet sign mean?

In addition to existing answer: Learning material I found later also adds another possible cause for amber light (see slide 41):

smoke is detected in a lavatory

so the amber one can also illuminate automatically.

Nice find. This is an optional feature, some B737 can have it and other not.

That should be mentioned in those flight magazines that always lay around - that would be some exceptional customer service! ;)

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text:
Are ATC radar tracking records and audio recordings considered legally public?
In practice, they are simply available online and mostly free.
Alternatively, anyone may purchase an ADS-B receiver to monitor the surrounding air traffic and air-band radio to listen to ATC.
I am wondering if there are regulations, similar to restriction of the use of GPS tracker and phone call recording? Or is it simply assumed that, for public safety, anyone conducting a flight is automatically presumed to volunteer the information of flight path and air conversation to the public?

I would assume, and to me it makes sense. It's not like that in every jurisdiction though, it's illegal in both UK and Germany to listen to ATC if you're not in an aircraft or in an ATC facility. It's stupid, but still illegal. Mode S receivers appear to be legal there too though, so at least it's only an old law that's surviving.

In US, I think it is legal to listen but requires a license to transmit.

"Public" isn't very well defined. You should ask for rights to listen, to disclose, to record and to publish. In a country you may have some but not all of them, they may be subject to various authorizations too. An obvious difference between a phone call and an ATC exchange is that one is a private communication with specific persons (and is protected by privacy laws), the other is not, but isn't fully public either, it is not intended to anyone who can listen to it. Add to this possible paranoid or genuine security aspects.

What I've always thought odd about UK and Germany is that you can't listen to ATC but apparently ADS-B is fine. That never made sense to me

@mins, the scope of public is yet to be discussed.  I mean the participants of air traffic control conversation have no right to claim its privacy and property, and the general public has the right to access them.

The FAA is only authorized by congress to regulate FLIGHT, not radio communications.
Radio communications are regulated by the FCC.
Both of these agencies have no power to make laws. They can make only "regulations". In the United States, according to the Constitution, laws can only be made by Congress or the legislatures of the several states.
The position of the FCC is that it is legal for any person to monitor and record any radio transmission that they wish. The only exception to this is listening to private telephone conversations or encrypted military transmissions. The Federal law that prohibits this, explicitly exempts maritime and aeronautical transmissions. This is the language:

18 USC § 2511 (2)(g.ii.IV) It shall not be unlawful under this chapter
  or chapter 121 of this title for any person to intercept any radio
  communication which is transmitted by any marine or aeronautical
  communications system;

Therefore, by United States federal law it is explicitly allowed and permitted for anyone to monitor and record maritime or aeronautical communications.

+1, very good answer for the listening activity. Anything for recording, disclosing, publishing? I assume disclosing is subject to conditions (e.g.  15 min delay). If CVR were transmitted live via satellite, could the cockpit conversation be broadcast on the Internet live?


text:
Is the location of the strake ( chines) on the two seat F-16 variant is the same as for the one seat one?
Is the location/length of the chines (the cobra hood looking) on the two seat F-16 variant the same as the ones on the single seat variant?
The two seat variant has a longer cabin, so it must be further until they meet the wing roots. Is the location of the vortices the same? To me they appear to be more forward on the single seat variant.

The premise of the question is wrong. The single seat and two seat variants of the F-16 are the exact same length. Other than that, it is not really clear what you are asking

I asked if the starting point and the end point of these vortex generators  are different one  from  another in single seat and two seat variant of the F16.If not how they influence the vortices at the roots of the wings.

Yes.  The location of the chines occupy the same fuselage station coordinates on both single and dual seat versions of the F-16.  The addition of a second crew members station in the aircraft necessitates the removal of a forward fuel tank, reducing the total internal fuel capacity of two seat F-16s.


text:
When the F16 is landing the AOA will be at 11 degrees, but speed modulates more. How is possible to have fixed AOA but not the speed?
The speed in landing pattern is not fixed one due to the weight/drag of the aircraft at the moment(loads of bombs and fuel). But if you speed up then you're going to go upwards don't you(if you keep the11 AOA) ? Because any changes in pitch increases the amount of the lifting force. See my point of view? If change one must alter the other. So if you're not happy with the glide slope (to steep or to shallow adjust the throttle (for F16 only) but automatically within that case the AOA will decrease or increase.

Using AoA as reference gives a simple way to maintain a safe stall margin. If approach speed was used as reference, there would have been multiple speeds to memorize, as the weight is not the same from mission to mission.
Remember, wings basically always stall a certain AoA, not certain speed. Specifying a AoA to maintain, the weight of the plane is automatically compensated for.
The pilot does not need to worry about speed. If he/she wants to go higher, add throttle, maintain AoA -> plane goes up. If one is too high, decrease throttle, maintain AoA -> plane descents. The airspeed is out of the equation, so simple. Just remember to keep AoA at 11 degrees.
As you stated, depending on mission, military aircraft have huge variation in takeoff and landing weights. They also have very reliable AoA metering, so it' s best to go this way.

Of course the wings stall angle will be 29 AOA for F16but you don't want to be at that attitude on touchdown(because scrape the tail on runaway and main wheels don't have any contact with the ground). F4 land at14- 17 AOA(has a enough clearence aft to do that). But not so much for F16

Yes. And you do not want to fly approach anywhere near stall AoA.

Correct that changes to one performance parameter will affect others, but it isn't totally clear what you are asking.
If you are in the pattern at 11 deg AOA and level flight you are in equilibrium.  11 deg AOA correlates to a certain airspeed at a given weight.
That airspeed will vary depending in weight, and the correct indicated airspeed must be for each landing weight and cross checked against the AOA gauge for accuracy.
If you “speed up”, you won't be at 11 deg any longer.  If you just pitch up, you will increase AOA, climb, and decelerate unless you add power.
If you are light, your airspeed will be lower at 11 degrees AOA than if you are heavy.  So, “multiple airspeeds to memorize” is partly true, but generally there are basic rules of thumb that make it easier:  For example, if you know your 11 deg airspeed at your base weight, you simply add fuel and stores weight, multiply by some factor, (in my case 1.5 Kias per 1000 lbs) then add this to the base approach speed.
The reality is that your “on-speed” approach and landing speed will typically only vary +/- 10 knots from “normal”, and the quick calculation plus fuel gauge accuracy probably has a tolerance of a few knots as well, so as long as airspeed is in the ball park enough to trust your AOA gauge, then that is what you use.

That's why I'm asking the question:how it's possible to do it (11 AOA) at different weights, alrports altitudes, and in summer and winter without alterning 11AOA?Jpe61 answer me.

The airspeed varies.  For each weight the pilot must calculate the correct indicated airspeed that correlates to 11 degrees.  That is how you cross check the AOA gauge accuracy.  Does that clear up your confusion?  Because if so I will edit the answer to emphasize that point.

P.S.  I went ahead and edited my answer to clarify and add details.  Please let me know if you have any further feedback or questions.

The original question states:

The speed in landing pattern is not fixed one due to the weight/drag
of the aircraft at the moment(loads of bombs and fuel). But if you
speed up then you're going to go upwards don't you(if you keep the11
AOA) ? Because any changes in pitch increases the amount of the
lifting force.

This is a flawed premise.
Any time that the aircraft is travelling at a nearly horizontal trajectory with a constant airspeed and vertical speed, lift is very nearly equal to weight.
Given these conditions, if we prescribe a target angle-of-attack, then we are essentially prescribing that the airspeed should vary according to the square root of any change in wing loading.  Any variation from this target speed will cause in imbalance between (the vertical component of) of lift and weight, which will cause the flight path to curve upwards or downwards.
If we are holding 11 degrees angle-of-attack, and our weight suddenly increases by a factor of 2 for some mysterious reason, and our airspeed increases by a factor of 1.4 for the same mysterious reason, no, we will not "go up". As long as the airspeed varies according to the square root of the change in wing loading, the forces on the aircraft can remain in balance.


text:
What is a mushing glide?

Source: Wolfgang Langewiesche - Stick and Rudder; An Explanation of the Art of Flying

Why is it called a mushing glide?
In this glide, does the aircraft point its nose less (or more?) steeply?
How does it steepen the descent?

I find the explanation confusing. At one point it seems that a mushing glide is caused by a high AOA and at another point it seems that a low AOA (pointing slightly above horizon) causes it.

I have not heard that term. Where is it from?

@TylerDurden From what I see, it is very similar or exactly the same as the touchdown flare.

seems that low AOA (pointing slightly above horizon) AoA is relative to the airstream, not the horizon.

For a glider, pointing slightly above horizon is high AOA because normal AOA is pointing below the horizon.

It is called "mushing" probably because the controls will be a little mushy (soft). At high angles of attack you begin to lose control authority and the controls can feel soft.
The nose will be pointed slightly above horizon.
When you pull back on the stick your forward velocity will decrease, but your rate of vertical descent will stay the same or decrease by only a small amount, so your angle of descent will become more steep.

Let's put some numbers on this and make a "real" example. Let's imagine you are in a sailplane which is in a configuration that stalls around 35 mph. You are currently travelling at 45 mph in a level flight attitude, descending at 150 feet per minute. You will be on 2-degree glide slope (confirm this for yourself). Ok, now pull back on the stick until you are going about 37 mph. At this point the controls will start to get soft. Your vertical speed may decrease to about 140 feet per minute. Your glide slope will increase to 2.5-degrees. Thus by this maneuver your glide slope increases (becomes more steep).
Just as a further exercise, let's compute how much we can change our touchdown point by the above maneuver. Suppose we are at 200 feet AGL, then we will touchdown in about 5200 feet in the beginning attitude (confirm this for yourself). Okay, now we pull back the stick to 37 mph ("mushing" descent to use Langewiesche's terminology) and our vertical speed goes to -140 FPM. How much does this change our touchdown point?
If you do the math, you will find our touchdown point changes from 5200 feet to 4650, a difference of over 600 feet. So, by using a "mushing" glide we have changed our touchdown point significantly. Let's just illustrate it with a real airfield:

So, here we see our current position at the circle. If we continue on our current glide path we touch down in 5200. It's too close to the crossover on the runway. We would much rather land at the blue line. By using a mushing glide we could accomplish that.

Great explanation. I guess I need to check for myself and "feel" the softness of control surfaces

@user2927392 If this answers your question, you may want to accept it. I would suggest doing the calculations I describe in my answer for yourself. Doing calculations like this will make you a much better glider pilot since you will know the actual real geometry of the situation, not just visual guesswork.

Yes this answers the question. I think I confused rate with angle.When you maintain pitch above the horizon, you actually decrease the sink rate but increase the sink angle. And I am correct, if you pitch slightly down, you increase the descent rate but you descend less steeply.

Why not make an S-turn or two to lose altitude, rather than bringing yourself dangerously close to stalling?

@Sean The question was about mushing glides. Normally to shorten the touchdown distance a pilot will use the dive brakes, or slip if a large adjustment is needed. It is a bad idea to maneuver on final.

According to See how it flies (https://www.av8n.com/how/htm/energy.html#sec-power-curve-intro), you don't just get the steeper angle of descent but the descent rate in feet per minute also increases as you pull nose up when in mushing flight. I think it's because at some angle of attack pulling back further starts to reduce the lift but increases the drag. The critical speed where you enter mushing flight is best-angle-of-climb speed.

Why is it called a mushing glide?

The aircraft is not cleanly cutting through the air. It is "mushing" through the air at a high angle of attack creating lots of drag and a slow forward airspeed.

In this glide, does the aircraft points its nose less (or more?) steeply?

The aircraft has its nose pointed up (less steeply) than a normal glide.

How does it steepen the descent?

The low forward airspeed and high drag creates a high rate of sink relative to the forward motion. Low forward speed and relatively high sink rate means the descent will be very steep. A fully stalled condition would be an extreme example of a "mushing" glide.

low AOA (pointing slightly above horizon) causes it.

pointing the nose slightly above the horizon is still a High Angle of Attack, not low AOA.

The maneuver described in the book minimizes the sink rate, so you have it wrong. To quote the book ("A sailplane--in fact any normally shaped airplane in a glide, will lose the fewest feet of altitude per minute when flown at this gait").

I guess it depends on how low the airspeed is. If you are on the edge of a stall, you will have a steep angle of descent.  Low forward airspeed causes a steep ANGLE of descent but a low RATE of descent.  It is sort of the opposite of best RATE of climb vs best ANGLE of climb.

You said in your answer that the maneuver causes a "high rate of sink". That is not right. A gliding aircraft's sink rate (vertical velocity) will be minimized by increasing the angle of attack. That is exactly what the book says (and the book is correct).

I edited my answer to make it more correct. "low forward airspeed and high drag creates a high rate of sink relative to the forward motion."

That seems like a weird way to say it. If you look at the numbers in my example which are pretty typical I am not sure if I would characterize that as a "high sink rate". To a glider pilot a high sink rate is -500 fpm. In a so-called "mushing glide", your sink rate actually decreases slightly, maybe from 150 to 140 or 130 at best. Also, the glide slope change is not really that dramatic. I have done this maneuver so I know. Just run the numbers for yourself.

The question was asking how a "mushing" glide steepens the descent. I guess I could have worded it better but I wanted to emphasize that the slow forward speed would produce a steep angle of descent even with a low rate of descent .

@TylerDurden: Mike is right, and a mushing glide does come with a high sink rate. Once you fly below minimum sink speed, sink rate goes up when you slow down. You may think you have flown this maneuver, but with that low sink rate it was not really a mushing glide. I've done real ones.

@PeterKämpf At the risk of repeating myself, the author of the book (Langewiesche) himself says sink rate is minimized, the words he uses are "fewest feet of altitude per minute". So, just to be clear the sink rate DECREASES when you pull back on the stick. I actually give practical  numbers in my answer. If you are saying sink rate increases after pulling back on the stick, you are controverting what it says in the book the OP cites.

@TylerDurden: Take any glider (I have made the best experience with a Discus; an ASW-20 is less docile) and fly it in a thermal. Preferably late in the day when the thermals are wide and smooth. Then fly the plane at an appropriate speed (90 km/h for 30° roll angle). Note the vertical speed. Slow down to 80 km/h, or to 75 (the Discus will do this without problems). Note the marked decrease in climb speed. Do it with water in the tanks and add 10 km/h to the numbers above. Same effect. What are we even arguing here?

@PeterKämpf How is this even relevant to the OP's question? You are kind cluttering Sowsun's answer. If you have your own ideas about interpreting the passage in the book, maybe you should make your own answer.

@TylerDurden: How ironic! After 5 comments you are concerned about cluttering Mike's answer. Well, then shut up. Both you and Langewiesche are wrong and Mike is right, short and simple.

authors: عبدالمنعم ابو كريم الديري


text:
What happens during a powered descent?
I was having a discussion with my friend about equilibrium condition in flight:
Scenario:
While going in straight and level flight, say I reduced my airspeed by 30 mph.
At the same time keeping the airplane's attitude strictly the same as before
(doing whatever it takes to keep the nose where it was before).
Reducing the speed means, the aircraft develops less lift: Aircraft is supported by less pounds of lift force (meaning which lift is less than weight)
What happens next? (imagining that pilot does not nose down)
My take:
1. Since weight > lift, aircraft drops attitude and falls like a stone that was dropped in midair unless the nose is down.
My friend says:
2.  The airplane finds new lift. This sinking motion creates lift
for aircraft. But it will not maintain straight level flight but descends. It will be a steady descent not accelerating descent. (not like a stone falling out of sky). He says this is called power descent
My question is:
1) Who is right here
2) If my friend is right, if aircraft can find lift after it descends (which means it found equilibrium) , why can not it maintain straight and level flight. And what exactly caused it to find new lift? Has angle of attack changed?

Maintaining fixed pitch is actually used in the unreliable airspeed procedure. When airspeed indicator fails, the usual procedure is to assume specified attitude (which corresponds to typical attitude during approach) and adjust power to achieve desired rate of descent (which must be no higher than normal approach).

Neither of you are necessarily right, but you both have some understanding which is accurate.
Let me reiterate what you have stated, for clarity's sake. The scenario starts with the aircraft flying straight and level. Then the airspeed is reduced by 30 mph through a power reduction while the attitude is held constant. Regardless of what else happens we all recognize that this will result in some type of descent.
You are right in that the airplane has lost "lift" from the lost thrust and will thus descend. Depending on the aircraft and the starting airspeed, you might be right that the  aircraft might respond with an uncommanded attitude pitch down. If that were the case, it would be due to the scenario resulting in an aerodynamic stall. However, even if the aircraft were to stall it would not drop like a stone (that is, with no lift to oppose gravity), but would descend at what would still be a substantial rate of descent while still producing some lift to oppose gravity. Moreover, considering the possible entry speeds and attitudes, a stall would be unlikely in this scenario.
Your friend is right in that, with sufficient airspeed and no aerodynamic stall—both of which depend on the airspeed at which the maneuver was started—this scenario will result in a descent. It would be accurate to call this a powered descent. Depending on what he means by it, your friend may not be quite right to think that any "new" lift would be produced by the sinking motion itself, but this might be a difference of semantics. Let's explore this further.
Let's consider a Cessna 172 cruising straight and level at 110 mph. We then reduce the power to maintain 80 mph and hold the pitch attitude exactly where we started. In this scenario we have transitioned from cruise speed to something closer to the aircraft's best rate of climb speed. This means that we have transitioned from a high speed, high drag region of flight to a lower speed, lower drag region of flight. At the same time, by holding the aircraft's pitch attitude constant, we have changed from a low angle of attack, low coefficient of lift region of flight to a high angle of attack, high coefficient of lift region of flight. This increase in angle of attack is due to the new angle of the relative wind introduced by the aircraft's descent. The overall amount of lift doesn't change, but the way the lift is created does change. As the speed is reduced the wing's ability to create lift (expressed by the coefficient of lift) increases with the increase in angle of attack. Thus the lift doesn't change, but the lift is now due more to the angle of attack than the airspeed. If this is what your friend means by "new" lift introduced by the sinking motion, then he is right.
However, this "new" lift must be understood to be due to the angle of attack change, not an increase in net speed (kinetic energy). The lift isn't actually changing, merely the way in which it is created—angle of attack as opposed to speed. However, if the scenario were different and we allowed the aircraft to pitch down as we reduced power, the aircraft would pitch down to maintain about 110 mph, and the wing's coefficient of lift would change very little as the airspeed and angle of attack remained relatively constant.

The lift would be the same, regardless of speed. In the low-speed case the airplane still weighs as much as in the high-speed case, so lift must be the same. Only in the transition between states it will change a little.

@PeterKämpf There, is that better? The coefficient of lift increases with the increase in angle of attack.

Let the upvote be my answer.

so what I understand is that when the aircraft descends maintaining same attitude, it increases angle of attack since the relative wind is meeting the wind from below and we are not pitching down. As a result of higher angle of attack, aircraft regains its lift and establishes its equilibrium. What I am not clear is that since there is 'some' thrust available, why does the aircraft keeps descending. Why can not it maintain level flight with this 'new' lift? Sorry if I missed this from your answer.

@user2927392 The issue is that by maintaining the same attitude throughout the maneuver you eliminate the option of increasing lift. If we were to instead pitch up beyond the initial pitch attitude we could increase our angle of attack sufficiently to increase lift to make up for the lost thrust.

Even if it does not increase lift, why does it not maintain level flight (since now that lift == weight). I am sorry if I am repetitive

@user2927392: The aircraft doesn't regain lift. It gains a bit of lift but less than what it lost. It descends because it loses more lift than it gains. Which is why I consider "regain" the wrong word to use.

@Peter Kämpf: If the airplane is descending, then lift must be less than weight, no?

@jamesqf No, in a stable descent the aircraft is in equilibrium and is not accelerating; lift equals weight.

The reason it keeps descending is inertia. When you decrease power and reduce lift the airplane begins to descend. When it comes back to equilibrium between weight and lift it will no longer accelerate downward but it will continue downward at the same rate. The original unbalanced force will start a downward motion. Once that motion is established and the forces are rebalanced it will continue in the same direction at the same speed until the forces change. To stop the descent you would need to make lift greater than weight until the descent stopped.

@jamesqf: Yes, but only slightly less. The rest is contributed by drag because the drag vector points slightly up in a descent. All other weight is carried by the vertical component of lift, and the horizontal component of lift is equal to the horizontal component of drag (assuming no net thrust from the engine).

Note: This answer refers to the initial question as asked by user2927392.
Who is right depends on the initial speed.
Lift  is determined by two parameters as long as the wing geometry stays unchanged, angle of attack and dynamic pressure (which is the product of air density and speed squared). The slower plane will initially develop less lift and start to descend, which in turn will increase the angle of attack such that the initial lift is regained. Since you want to maintain the attitude of the aircraft, its sinking motion will mean that the airflow comes in more from below. Note that we speak of very small angle changes - just a few degrees normally.
Now much depends on how close the aircraft was to its minimum speed. As angle of attack increases, the flow will have trouble to follow the steeper contour of the wings and start to separate. If this separation grows, it will limit the lift the wings can produce. Now we have two cases:

If the initial airspeed was higher than minimum airspeed + 30 mph, your friend is right. The aircraft will settle at a new angle of attack and will compensate the missing thrust with a gradual altitude loss, just as in SMSvonderTann's answer. Like a glider, the airplane will glide down to the ground. I assume you intend to keep the nose up by pulling on the stick: This will trim the aircraft to the lower speed and a higher angle of attack where it settles at the new equilibrium.
If the initial airspeed was lower than minimum airspeed + 30 mph, you are partially right. The aircraft will stall, lift will not suffice to find a new equilibrium, and the airplane will pitch down to pick up the missing speed, no matter how hard you pull. If you still insist on lowering the speed, you will now pull out of the dive and repeat this maneuver all over again, until the ground interfers. Note that the resulting motion is not a continuing dive, but a sequence of "J"-shaped curves when seen by an outside observer. The dive is less a vertical plummeting than a steep glide, similar to a rollercoaster.

To answer your second question: Drag will slow down the aircraft unless some energy is continuously furnished by reducing altitude. Please read this answer which has a detailed explanation, albeit for paper aircraft, including some fancy math.

Are you worried that someone will change the question? I rolled the edit back to match the original question. I didn't change the question.

Your friend is right. The airplane is basically a glider in that scenario and gliders still fly even though they are mostly unpowered of themselves, motor-gliders excepted.
The airplane can find lift as it descends because of the gravitational potential energy it has. However, the lift produced is less than the weight of the aircraft, due to drag and the Laws of Thermodynamics (The First and Second if I am not mistaken) so the airplane starts to descend. The lift is caused by the airspeed as the potential energy of the "dropping" plane converts to kinetic energy and thus airspeed and lift along with it. You could find net positive lift by flying into a rising thermal like a glider does to bring it higher.

Hey, downvoter! This answer is not wrong, just incomplete. No need to downvote it!

Let's generalized where the airspeed is any X, where X >> 30 kts and that X << Mach 1.
If you were level and you reduce the power and touch nothing else, the aircraft will descend and accelerate until it reaches roughly X again; the point of equilibrium between angle of attack and airspeed. The aircraft will descend with roughly the same airspeed as what you started with.
This effect is critical in landing. Adding power reduces the descent and reducing power increases the descent; without significantly and over the long term changing the airspeed.

The question stipulates maintaining attitude.

I think you (and some of the answerers) are making this way more complicated than it needs to be. These are the facts:
(1) If you are in level flight and you reduce power, you will descend. This is the normal way to descend.
(2) If you are in level flight and you push the yoke forwards, you will go faster.
(3) If you are in level flight and you pull the yoke back, you will slow down.
That is all there is to it. Don't make it too complicated.


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What is the purpose of sum voltage monitor?
I was looking at the design diagram of actuators.
Every channel of the actuator is connected to a voltage differential transducer. The transducer outputs are fed to a sum voltage monitor. I could not understand its purpose.
How can summed voltage exist if there is a single sensor? Or am I missing something here?

Can you perhaps reference that diagram?

Added figure reference

Where did you get that fragment of a drawing from, and what do "REU", "PCU", etc. mean? Note the LVDT is not connected directly to the SVM on your diagram, we have no idea what processing is going on in between. My guess is an error signal (meaning the difference between the desired and measured position) is being produced somewhere in that path for controlling the surfaces.

By the way the SVM may be subtracting the LVDT's reported position (solid line from the side of the LVDT) from a commanded position (dashed line coming, I guess, from the cockpit) so it may be monitoring the error there. I have done some control theory, but not familiar with avionics and the standards and jargon used here.

Please add some references like the aircraft type, type of control surfaces we're talking about (I suppose we're talking about spoilers here, given the presence of an "Engage logic" block), etc.

Its Bombardier c series. Reu is similar to ACE. It commands the pcu.

Are you sure that SVM means Sum Voltage Monitor?

Yes.I think I found the answer. LVDT has two voltage outputs. Those two voltages are added and compared against predefined thresholds.

"In an exemplary embodiment, a sum of secondary voltages V1 and V2 from a transducer is obtained by adding the secondary voltages together, i.e.; V1+V2. This sum of secondary voltages theoretically should be constant for all LVDT/RVDT positions, since the total length of the secondary transformer is constant." (patent: Detection of faults in linear and rotary voltage transducers)

It compares the commanded position with the actual position, it is the standard feedback loop.

Thanks for digging up an answer for this old question! Would you please include some references (links if possible) to support and improve your answer.

It does provide an answer to the question.


text:
Will the ATC be in constant communication with aircraft?
When a passenger aircraft travels at higher altitudes will it be in constant touch with air traffic controller?
Are the altitudes or flight levels assigned by ATC or does the pilot file them as part of flight plan?
While flying over regions with no radio communication, how does one ensure that there are no other aircraft nearby?

You are asking three different questions. All of them have been answered here: http://aviation.stackexchange.com/questions/26727/is-it-required-for-pilots-to-contact-atc-while-flying-vfr/30891#30891 / http://aviation.stackexchange.com/questions/31599/does-atc-direct-flights-to-fly-eastbound-at-odd-levels-and-westbound-at-even-one/31606#31606 / http://aviation.stackexchange.com/questions/492/how-are-aircraft-separated-in-a-non-radar-environment/32460#32460

@J.Hougaard but this predates the second one you list

Generally speaking airliners are always able to be in contact with ATC, either by VHF (regular radio), HF (usable over longer distances, e.g. on oceanic crossings), or satellite communication (possibly relayed through their company dispatch). It is also possible for one aircraft to relay messages for another (for example if one aircraft's HF radio has failed they may contact a nearby aircraft on VHF to relay messages to ATC).
Because they can usually talk to ATC even when they are out of radar contact airliners can and will provide position reports, and ATC updates their position information the old fashioned way (which we talked about over here). The controllers can then assign altitudes, speeds, and headings/routes in such a way that no two aircraft attempt to occupy the same piece of sky at the same time.  (This is generally the way oceanic routes are handled. There are also air-to-air frequencies for aircraft flying these routes so they can coordinate with each other if necessary.)
In the event an aircraft is out of contact with ATC - whether through a radio blind spot, an equipment failure, or for some other reason - they rely on a combination of lost communication procedures (here's a quick reference from the FAA) and "see-and-avoid" (if you see another aircraft avoid hitting it) until contact can be re-established.
The use of standard lost communication procedures also allow the controllers to continue updating the aircraft's position in a non-radar environment (they can estimate progress based on the standard procedures and the aircraft's prior position reports/speed/wind data). A larger block of airspace will be reserved in such situations to account for any error.

You know,  "if you see another aircraft avoid hitting it", just seems so intuitively obvious that it shouldn't even need to be said, but, human nature being what it is...

@FreeMan Don't forget it is also human nature to start panicking when something unexpected happens. Avoiding another aircraft requires staying in control of oneself in the first place.

At high altitudes one in never out of radio range for ATC. The usual VHF airband frequencies only work within line-of-sight, but if you're too far away for that, one can switch to HF radio which follows the curvature of the Earth.
Most parts of the oceans are outside radar coverage, so the controller cannot see where you are. In these areas ATC depends on position reports from pilots for separating flights.
Flight plans contain a requested cruising altitude, which ATC will generally clear the flight for if possible, but when traffic requires it pilots have to take what ATC assigns.

"At high altitudes one in never out of radio range for ATC" There are a few oceanic routes where there is no ATC contact.

Alaska also has high altitude routes that have no ATC or radar


text:
Why does the J58 engine of the SR-71 have a diffuser after the inlet spike?
I heard that the diffuser allows the compressed air after the inlet spike to "spread out". What does this mean? If this means expansion, wouldn't it be beneficial to have it compressed before entering the compression chamber, so why would it spread out?

Exactly for what you think is beneficial: To increase pressure and, as a consequence, create the majority of thrust at Mach 3.2. The nozzle is adding less than half of total thrust.

Generally, a compressor cannot work efficiently at supersonic speed due to the shockwaves, the role of the inlet cone and diffuser is to slow the air below Mach 1. There is a similar need for a ramjet, so that the combustion can occur within the engine and produce thrust.
The cone position and diffuser geometry are adjusted according to the airspeed. The overall shape of the diffuser is diverging.
From Bernoulli's principle, the diffuser decreases velocity and increases pressure according to:
$\frac 1 \rho \; dp = - \mathrm V\;d \mathrm V$ where $\rho$ is air density.
Look at this video: Converging Diverging Nozzles for more details about how pressure and velocity are affected in a nozzle / a diffuser. Here is a summary:

The J58 is turbojet within a ramjet. The forward section of the engine has a complex role. It adapts to a large range of speed (0 to Mach 3.2) and altitude (0 to 85,000 ft), and modifies the airflow to work either as turbojet, or as a ramjet, depending on the airspeed.

Simplified adjustment of the airflow (source).
Actual mechanism used at different airspeed ranges in the J58:

(Source)

Actually, the task of the diffusor was to create thrust. Sounds strange? Then read on!
At supersonic speed the spike ahead of the inlet will create a cascade of ever-steeper shocks in order to slow down and compress the air. Inside, the cross section narrows down further until the flow is decelerated to below Mach 1 in a final, straight shock. This is the point of the smallest cross section, called the throat. Falling to subsonic speed fundamentally changes the behavior of the flow: When before, at supersonic speed, it would slow down in a narrowing cross-sectional profile, it now needs a widening cross-sectional profile to slow down further. As it slows down, the kinetic energy of the flow is converted to pressure, so at the compressor face the flow is only Mach 0.4 fast, but has almost 40 times ambient pressure. Note that this is about the pressure ratio of modern jet engines like the F120 or the GE90 and way above the pressure ratios of 1950's-era turbo compressors.
By moving the cone, the position of the throat is adjusted such that the intake works over the full flight speed range. From subsonic to Mach 3.2 the capture area increases by 112% while the throat width is narrowed to 54% of its subsonic value.
The diffusor is needed to slow down the subsonic region of the intake flow. At the same time it is filled with high-pressure air which pushes at its walls. The pressure acting on the projection area in flight direction is contributing the majority of the total thrust of the J58. The job of the engine is to suck away the air in the diffusor and to eventually accelerate it back to flight speed and above. Without the engine, the same pressure would be acting on the rear wall of the diffusor and would cause massive drag - the engine had to pump all that air away to avoid this to happen.
I think the claim of 80% thrust made on this page is not quite true, but it illustrates the point.

At Mach 3.2 cruise the inlet system itself actually provided 80
  percent of the thrust and the engine only 20 percent, making the J58
  in reality a turbo-ramjet engine.

A little down, it presents us with more credible numbers:

At Mach 3, the inlet itself produces 54% of total thrust through
  pressure recovery, the engine contributing only 17% and the ejector
  system 29%. The compression ratio at cruise is 40 to 1.

Also, the reason to call it a turbo-ramjet is actually a different one, as given on this page:

The SR-71's Pratt & Whitney J58 engines were rather unusual. They
  could convert in flight from being largely a turbojet to being largely
  a compressor-assisted ramjet. At high speeds (above Mach 2.4), the
  engine used variable geometry vanes to direct excess air through 6
  bypass pipes from downstream of the fourth compressor stage into the
  afterburner. 80% of the SR-71's thrust at high speed was generated in
  this way, giving much higher thrust, improving specific impulse by
  10-15%, and permitting continuous operation at Mach 3.2. The name
  coined for this configuration is turbo-ramjet.

Please note that all the diagrams which show air flowing from the diffusor directly to the afterburner don't get it quite right: Some air was needed for cooling, but also the first four stages of the compressor were still involved, and the remainder of the turbo machinery also had to be working at Mach 3.2 to supply the compressor with torque. The J-58 took compressed air from the compressor at stage 4 and piped it directly into the flow aft of the turbine. This cooled the exhaust stream that entered the afterburner, so the starting temperature there was lower and the density higher, which increases efficiency and thrust. See the thick black tubes in the J58 picture below (source) - those piped the compressed air to the afterburner.

All supersonic intakes use this principle: See below for a breakdown of thrust contributions inside the Concorde's Olympus 593 engine and nacelle:

Concorde nacelle cross section and thrust breakdown (picture source)

Saying that the inlet contributes 80 percent thrust and the engine just 20 sounds weird to me. Because while the diffuser is the main action point of the force (in subsonic engine, the compressor is), the force still only exists because of the hot section behind it. There couldn't be any thrust without the energy provided by the combustion. So it is still the engine that produces the thrust; just it acts in the compression section, because that's the one with significant rear-facing surface for the pressure to act upon.

@JanHudec: Yes, absolutely. Only when you integrate the pressures inside will the diffusor be the main source of thrust, and it only can be because the engine lowers the pressure at the end of the diffusor by pumping all that air away. When you look at the momentum change, the diffusor will slow down the intake flow, thus reducing thrust. Only because the engine can accelerate that slow flow again do we get positive thrust.

After some years, I now finally understand what people mean by "intake produces thrust" when referring to supersonic cruise aircraft like Concorde or the Blackbird, thank you.

thanks to @PeterKämpf and jan hudec for clarifying this "intake produces thrust" business for me! I have struggled with this for years and now I, like Talisker, finally get it!

The reason for the diffuser is this....the spike slows the air down to subsonic around Mach .8 . The diffuser further slows the air to around Mach .4 before entering the engine inlet. It’s the same concept as a pressurized water hose going from 1/2” size to 2”. Allowing the air to expand slows it down but it maintains pressure by sheer volume. I was a jet engine mechanic for 10 years (not on the SR) and love discussing this incredible engine system. I am happy to share any info that I have learned about this .


text:
Does slipstream on a single engine aircraft create a slight difference in wing strut loads during TO and Climb Out?
If right rudder is used to counter yaw caused by propellor slipstream that hits the fin, does that same slipstream try to lift the left wing and push down on the right wing? If so are the strut loads slightly out of balance during take-off and slower portion of climb out?

Yes this is happening, but it isn't a big deal because you level the wings and side loads (or differential loads) is in the limit.You see that on landing, one wheel touch before the other.

Touching down with one wheel first has nothing to do with this...

Well, think it through - if you have such forces that create asymmetrical lift effects, this would result in a rolling moment.  If you have a rolling moment, you will be applying aileron to counteract the rolling tendency, and the aileron application will cancel any asymmetrical lift effects in stopping the roll.
So the answer is, if the airplane is in a symmetrical configuration, that is, ailerons neutral and wings straight, it's possible to have rolling moments present from slipstream effects near the wing roots that could induce a mild rolling tendency due to slight differences in local angle of attack.
Assuming it's enough to roll the airplane, if you didn't do anything, you would in theory measure slightly more tension on the upgoing wing's lift strut and slightly less tension on the downgoing wing's lift strut, while the rolling axis acceleration is present.
However, you're not going to let it roll, you're going to apply aileron to stop the roll, and this will cancel out any lift differential that was present, as far as the lift struts are concerned, because the aileron application to stop the roll has equalized the total lift of the left/right wings.

The two solutions that  engineers came with :1engine is not not aligned with longitudinal axes, 2 one wing incidence angles is bigger than the other wing.


text:
Is it pragmatic to use slats and flaps to maintain position of center of lift?
I am coming to this with an amateur understanding of CL, Cp and their contribution to the overall lift of a wing, so bear with me :)
I have been wondering for some time about whether you could design a system of slats (perhaps multiple stages of them) that deploy in tandem with flaps as to prevent the nose down pitch moment experienced on a typical wing when flaps are deployed. The idea is to bring the leading edge of the wing forwards and down, to extend the overall chord length, and in turn bring the relative aoa back to what it was before, but with a much higher cl-max (and of course lots of drag)?
The main idea behind this is that it would be very useful for canard aircraft if deployed on both the main wing and the canard. In theory it could greatly reduce the minimum speed and distance for takeoff without changing the lift ratios or messing with the cl/cg relationship. It seems like an elegant solution and I am puzzled as to why no one has done it yet? Am I missing something?
I apologise if this doesn't make sense. As I say, I'm still getting to grips with the concepts.

"I am puzzled as to why no one has done it yet? Am I missing something?"  What you seem to be missing is that every major jet airliner has both leading edge slats and trailing edge flaps.  So yes... it has been done, often and successfully.  (unless I'm missing something in your question?!)

I have been wondering for some time about whether you could design a system of slats that deploy... to prevent the nose down pitch moment. The idea is to bring the relative aoa back to what it was before.

The main purpose of a leading edge and/or trailing edge device is to change the camber of the airfoil. Without entering in physical/mathematical details, it can be shown that, going from the leading edge toward the trailing edge of an airfoil, the contribution of each piece of its camber to the aerodynamic force is proportional to the following plot/equation (my own plot of the function $\sqrt{\frac{x}{1-x}}$):

There it can be seen that the contribution to the aerodynamic forces of the forward part of the camber is basically negligible while it is the 30-something% most rearward portion of it which almost entirely contributes to the aerodynamic forces.
This explains why spoilers, ailerons, rudders, ... whatever surface used to change the aerodynamic forces is placed toward the end of the airfoil and not at its leading edge. This also tells us that any leading edge device like slats does not alter significantly the aerodynamic forces: slats are indeed used to improve/extend stall characteristics at high AoA but have almost no impact on the (slope of the) lift or on the pitching moment (source):

The main idea behind this is that it would be very useful for canard aircraft if deployed on both the main wing and the canard

In a lifting-canard configuration, flaps are only sparingly (or even not at all) used on the main wing because in a lifting-canard configuration the main wing normally lies quite backward and therefore any aerodynamic force created there possesses a big leverarm in respect to the CG: using powerful flaps on the wing would create a lot of pitching moment which should be counteracted by the canard which would then need to be designed bigger/heavier/draggier i.e. the opposite of why a canard design had been chosen in the first place. This is why in a lifting-canard configuration flaps are normally placed only on the canard itself and with fancy constructions.

Do you have a source for the image? Maybe I'm misinterpreting, but it looks opposite to the force distribution I normally see for example in this answer

@ROIMaison: the picture is my own work of the function $\sqrt{\frac{x}{1-x}}$ made under desmos.com. That function gives the lift due to camber for the thin airfoil theory, it can be found in any aerodynamics book I suppose, I'm quite sure that Mark Drela cover it in his book.

I'm still confused if I understand the plot. Is it the distribution of lift over the chord? Then I don't think it's correct, most of the curvature is at the front, so I expect most of the forces to be located there. This also matches airfoil pressure plots at 0 deg; like this

@ROIMaison: I've checked - Mark Drela gives a slightly different equation than the one that I wrote for the contribution of the camber, i.e.: $C_{l_0} = 2 \int_{0}^{\pi} \frac{dZ}{dx}(cos\theta -1), d\theta$. Here $\frac{dZ}{dx}$ is the slope of the main chord (aka the camber) and the weighting function is $(cos\theta -1)$ which, between $0$ and $\pi$, has a similar influence of what I've plotted in my answer.

Thanks for the explanation and reference! I found the relevant text and will check. I think it the plot is too much of a simplification to drive the explanation. The moment any angle of attack is added, the lift distribution over the chord looks very different.

Flap pitching moments are normally nose down with extension, although some airplanes pitch up with flap because nose-up trim changes from increased downwash on the tail overpower the nose-down trim changes from the main wing's camber change and aft pressure distribution shift with flap extension.
In sailplanes with flaps, this nose-down with flap extension dominates because the flaps have minimal trim change influence on the T tail of the glider from downwash, and the effects apparent to the pilot net out as nose down pitching moment effects on the main wing. So flaps down pitches the nose down, and flaps up (including reflexed above neutral for high speeds) the opposite.
Anyway, in canard-land, the Beech Starship got around the pitching moment changes from flap extension by variable sweep of the canard, about the most elegant way to deal with the problem, and alternatives using compensating aerodynamic surfaces on the wings sound like a lot more complexity than needed. As it was, the Starship was such a train wreck it nearly bankrupted Beechcraft.
Rutan's homebuilt canard designs didn't use flaps, largely to avoid having to use a variable sweep canard surface, a bit much for such homebuilt, and only have a speed brake under the fuselage. They are definitely not STOL airplanes.
And that's the rub, and the reason the configuration is so rare. The canard concept, like the flying wing, is an aviation dead end as anything more than a specialty configuration, with more negatives than positives outside of very specialized uses.

Do not focus on the slat alone, you have to keep the whole system in mind.
Slats generate lift ahead of the c.o.g., but they also deflect the air downwards (Dumping velocity). The incoming air thus hits the wing-element at a lower (or negative) effective angle of attack, thereby reducing the suction peak and delaying stall.
Look at this image from A.M.O. Smith's paper "High lift Aerodynamics", a highly recommended paper if you want to learn about the workings of high lift devices.

Several things are happening:

Lift generated by the slat (reduces pitch down moment)
Suction peak of the wing gets reduced (increases pitch down moment, as there is less lift ahead of the C.O.G)
Lift of the wing gets reduced (depends on exact effects)

The net moment delivered by the slat is influenced by its effect on the lift distribution of the wing, and therefore rather limited.

There are two answers to what you are asking, here:
Slats are not used for this, as slats have very little effect on coefficient of moment. There is no aircraft (that I'm aware of, at least) which uses slats for control forces in general, nevermind for trimming centre of lift. Their use is in enhancing overall lift force by preventing stall rather than being a lifting or control device in themselves.
This makes sense even just from the rule-of-thumb of a wing's aerodynamic chord line being 25% from the leading edge; even if leading and trailing edge surfaces produce the same forces when deflected the same, a trailing edge surface will produce several times more torque, and therefore provide the desired control with a fraction of the structure and machinery.
Flaps however, are used for this, though not commonly. The A350 is the main and most prominent example; rather than performing cruise trim with fuel movement, as the A330, A340, and A380 (and Concorde) do in order to minimise trim drag, the A350 can adjust the retracted position of its flaps.
Using a combination of trimming flaps, the horizontal stabiliser angle, and elevator angle, it is able to achieve comparable cruise efficiency with suboptimal centre of gravity as the older aircraft are, without needing the extra fuel tanks and pumps, and the reliability concerns they present.
The fuel movement system likely is superior in absolute performance, but weight and reliability savings presented mean that Airbus did not continue the system in their newest design.
You can find some airliner nerds discussing the switch here.

+1 for the link to the nerds' conversation! And, welcome to Av.SE.

The 787 had the variable camber system first, eliminating the trim tank. The A350, and 777X then got it later.

Right at the moment when flaps are deployed, we actually experience a nose up movement, at least in the planes that I've flown so far.
Anyway...
Remember that drag is a side effect whenever we want to generate lift so if you now don't increase the lift (by increasing any combination of thrust and AoA) then, yes, the plane will eventually lower its nose (more than you'd want it to).
However, flaps also change the camber so my understanding is that if the CoP is not shifted, the "new airfoil" might not sustain itself like the previous one, so you have to have the CoP shift - because the CoG is shifting too. Flaps have weight so when they stick out of the wing, the CoG shifts a bit rearward.
The positions of the CoP and CoG with respect to each other affect the pitch of the aircraft (and therefore also the AoA), so if one moves the other might need to too. Not saying that their relative positions should be the same but you need to be able to shift the CoP w.r.t. the CoG. Forcing the CoP to retain its original position doesn't really help- you need to make adjustments depending on what you want anyway. Flaps usually go out more than slats, so the net weight shift is towards the aft.
So far, the above is only with respect to non canard aircraft.
Looking forward to more answers by other people as well.

The answer is yes, slats can be and commonly are combined with flaps to produce essentially a high lift cambered wing, ideal to reduce airspeed required for lift by increasing coefficient of lift.
The slats can help maintain center of pressure in the wing but ...
there is also the effect of changing wing configuration on the airflow over the tail to consider.
Cessna ingeniously added this effect in its simple flap design of the 172 model.  While extending flaps will shift wing Cp rearwards,
it also increases downwash on the tail.  With its much longer lever arm, the net torque effect (around the center of gravity) is a pitch up.
As pitch is a result of aerodynamic forces, a variety of factors can affect it.


text:
Do GPS coordinates of a fixed point in space ever change?
As I understand, GNSS uses the WGS84 model of the earth to pin-point points in 3D space. However, once the GPS coordinates of a point in space have been determined (say a GPS waypoint), do it's coordinates ever change due to correction of errors in pin-pointing/triangulating the position? If so, how often would that be expected to occur?
That also begs the question, how are GPS coordinates of a fixed point in space found: by calculations and plotting the point in the WGS84 model or using satellites (just like the coordinates of the moving aircraft)?
For example: Say point A has the GPS coordinates 20.21457N 46.87453W. Will these numbers, once calculated, always point to the exact same point in actual space or will some sort of error correction ever cause these numbers to change (in order to continue pointing to the same intended point in actual space)?
My intuition says they don't change, because [considering] the actual earth and the GPS model of earth aren't changing in their shapes so a fixed point in 3D space with relation to each model should stay the same. Does anyone know any differently?

Oh, the earth is changing constantly....  Slowly, but change it does.

@Lnafziger For sure! My intention was to emphasize on "slow"! :-P

When you say point in space, do you mean coordinates on the surface of the earth, or a satellite's point "in space"?

I'm almost sure you mean WGS84 but i didn't want to just change it for you.

@MichaelHall Space = 3D space. Could be in the ground, could be in the air as from aviation's POV, we care anout the lat/long and alt of a point to refer to it in 3D.

I guess you did say specifically "do it's coordinates ever change due to correction of errors in pin-pointing/triangulating the position", that's clear enough.  Some answers seem to have missed that.  In other words you are saying they are fixing an error to make the reported position more correctly match the position on the WGS84 model.  Might be more clear to insert the word "published", i.e. "do its published coordinates ever change".

I'm still waiting for someone to find 120º N...

@grumpy1arrival silly typo LOL

The coordinates of a fixed point on earth do change, but they do change very slowly.
WGS84 is a coordinate system. It is based on an ellipsoid that approximates  Earth's shape.
The surface of the ellipsoid is the vertical datum of coordinate system. Heights in WGS84 are measured with respect to the ellipsoid ("height above ellipsoid" or HAE). It is important to note that the surface of the ellipsoid does not coincidence with the surface of the earth nor with the mean sea level.
Horizontally, position is determined as two angles. First the latitude, the angle between the equator, centre of the ellipsoid and the position and the longitude, which is the angle between the projection of position on the equatorial plane,the centre of the ellipsoid and the prime meridian.
The location of the prime meridian is chosen to be in Greenwich, close to the prime meridian of the Airy 1830 ellipsoid. (The difference is ~100 meters,reason for the offset has to do with local gravity direction offset and how time UT1 is defined).
Within the WGS84 coordinate frame, every position can be expressed exactly. GPS coordinates are by default expressed is WGS84 coordinates, but some GPS receivers allow output to be configured for different coordinate systems.
But the shape of the earth is not constant; due to continental drift and tectonic plate movements, coordinates of "fixed" positions slowly change. It is agreed that:

The International Reference Meridian and Poles and, hence the WGS84 datum, are stationary with respect to the average motion of the Earth’s crustal plates. As a consequence, all individual locations are in motion relative to them.

Source: thegreenwichmeridian.org
According to that website, in the UK, latitude and longitudes are changing by approximately 2.5 centimeters per year.

In addition to changes in continental positions, GPS itself is changing as well. GPS is not perfect, like every measurement system is a limited accuracy. So when you fix a GPS receiver to a position and record the position output over a longer time,you will notice that the position output is wandering around. It is somewhat random, but very strongly correlated over an approximately 12 hr period.

From the comments I see that you are wondering if positions of fixed points in aeronautical databases do change over time. The answer is: they do. It is rare, but sometimes waypoints do get moved, errors are corrected and routes and procedures do change. Hence the requirement to keep your GPS database up to date.

An example: due planned works near the threshold of a runway, the published threshold of that runway may be displaced temporarily to ensure a safe clearance height above the works. This will result in an update to the aeronautical database.
If that calculation of the new threshold was wrong, and the updated threshold point is not on the centreline but on the runway edge, another update is required.
If the update is not applied (because it was not picked up by the database provider), and subsequently the pilot relies on both the GPS being accurate and the database being correct, and continues to land based solely on GPS guidance despite this being a non-precision approach and the visibility is too low to see anything, the aircraft may land on the edge of the runway and crash.
A far fetched scenario? It may sound like it, but it actually happened.

Great answer! So even if the physical/geographic point on the earth's surface hasn't changed yet, the GPS coordinates can still change as corrections to previous satellite-based coordinates are realized.

@PapaMike99, I don’t think that is what is being said. Errors are corrected, but the coordinates of a fixed location on Earth is not changing. A waypoint that is ‘moved’ is not at the same original location. Also, it is the navigation database that must be kept up to date.

@PapaMike99 not necessarily satellite-based coordinates. As an example, the position of many points in the database were never measured, but instead calculated w.r.t. to measured points. If a calculation error is made and this is discovered, it will be updated in a next release of the database. So a waypoint in version 1 of the database may have different coordinates than the same waypoint in version 2 of the database. I've added an example.

@DeltaLima, excellent example! To be clear to PapaMike99, the coordinates of the runway threshold were incorrect as provided by the ANSP in the AIRAC supplement. The actual coordinates of the threshold did not change. This wasn't a change with the WGS-84 coordinate system, but an errant calculation that led to incorrect coordinates being published.

Re -"So when you fix a GPS receiver to a position and record the position output over a longer time,you will notice that the position output is wandering around. It is somewhat random, but very strongly correlated over an approximately 12 hr period." -- I didn't realize till just now that the deleted spam answer apparently copied this content directly.

@Timbo Thanks for all the input! Yes, we're on the same page here, it's just hard to put some stuff in words here :-P

Does the GPS coordinates of a point fixed in space change with time?
The GPS uses a coordinate system which is Earth-centered and Earth-fixed (ECEF). Coordinates are fixed to the average Earth (defined a bit later), which moves in space. Thus the GPS coordinate system also moves with Earth. If a point is fixed in space, it moves with respect to the GPS coordinate system, and its coordinates change continuously. I guess you're not asking for this trivial case, rather for the case the point is fixed with respect to Earth.
This steadiness is relative, for instance the Eiffel Tower has apparently a fixed position on Earth. But actually Paris is part of the Eurasian tectonic plate, which slowly drifts over the top of Earth mantle.

(Source).
To illustrate with an example, this plot is the progressive easting component of the drift at a GPS reference station in Bahrain:

(Source)
Static vs. dynamic coordinate systems
Thus the tower, like any landmark on Earth, moves with respect to other tectonic plates. Whether this motion should appear on maps is usually a State choice, and in the past the choice was simply to consider the local plate as fixed, even the plate deformations were simply ignored, because the physical network of geodetic markers was not accurate enough to show a difference.
Coordinate systems can be static or dynamic:

Static means the system moves with the local plate, measures done in this system are done against geodetic marks moving with the plate. The measure is constant when the plate moves, the only condition is to measure a feature located on the same plate.

Dynamic means the coordinate system is relative to a mean Earth: Plates have velocities in various magnitudes and directions (the cause of volcanoes and Earthquakes). Velocities also vary within a plate as it deforms. The mean Earth has a motion which is the average of all plates motion.

The GPS coordinate system is one fixed to this mean Earth, the mean Earth is considered fixed and all plates move and deform with respect to it. It means landmarks have GPS coordinates changing with time unless they move exactly at the mean velocity. This change is a good indicator of the tectonic drift.
Example and consequences of GPS coordinate drift
At 45° of latitude, 10 cm east-west are represented by about $\small 3.3 \times 10^{-7}$ degree. Coordinates are usually not available with this precision. But drift accumulates and with time it becomes apparent even to smartphone GPS.
As visible on the picture above, Australia is a country where tectonic drift is one of largest, about 7cm per year. The government used to create local maps in static coordinate systems fixed to the plate (up to GDA94). In spite of intra-plate deformations, coordinates remained constant. In recent years, the generalization of accurate GPS receivers revealed a significant discrepancy between GPS (WGS84) and GDA94 coordinates. This motivated Australia to reduce the divergence with an interim static system (GDA2020) and to later adopt a dynamic coordinate system. GDA94 coordinates were reassigned to GDA2020 locations distant from 1.8m in average.
GPS coordinate system (WGS84)
WGS84 system is not based on latitude, longitude and altitude coordinates. Instead it defines points in usual 3D coordinates XYZ (the green axes below):

(Source).
XYZ axes are Earth-Centered and Earth-Fixed (ECEF). The center is the center of mass. At any time the XYZ coordinates can be converted to latitude $\small \varphi$, longitude $\small \lambda$ (purple line) and ellipsoidal height $\small h$ using the ellipsoid shown. This ellipsoid is a good simplification of Earth oblate sphere at sea level.
Altitude is a matter a bit more complex, as it has been also with traditional surveying, the vertical reference being in general a distinct system, with its distinct benchmarks. Altitude is the height above the mean sea level. Water surface, discarding other factors like currents and winds for simplification, always align on a surface of equal gravity. Gravity in turn is mostly influenced by local density. Thus the surface of equal gravity is irregular, and so is the sea level. There are differences of about 200m in the distance to the center of mass.
The ellipsoid is close to the mean sea level, but is a perfect oblate sphere. The WGS84 coordinate system includes a model of gravity, EGM2008, describing, among other things, the height of the surface of equal gravity corresponding to the mean sea level, the geoid. The model provides the geoid height with respect to the ellipsoid. This height is added to the ellipsoidal height of the point to determine its altitude MSL.
How do we use a traditional coordinate system
Everybody use “datum” (like in North American Datum 83) as a synonymous for “coordinate system”, but there is a difference:

A coordinate system is a mathematical set of models and transformation formulas. It is useless to field people who need to determine the coordinates of some landmark. For example, in a traditional system, latitudes are counted with respect to meridian 0 by Greenwich observatory. That's irrelevant when someone determines the coordinates of a bridge in Chile.

In contrary a datum is the realization of the system, traditionally materialized by geodetic survey marks and monuments. These marks are organized in networks, with a first order of a few but very well surveyed marks, using different methods. The corresponding coordinates are published. A second order network build from the first one, densifies it. Possibly finer networks are created, so that the final user (a surveyor) can directly aim at close physical marks to determine the coordinates of a new location by triangulation.

By construction these datums are fixed, the coordinates of the marks are not updated, any location determined using such datum is final.
How does that scheme translates to the GPS coordinate system? Where is the WGS84 datum?
WGS84 realizations: Frames
For the GPS, the first order network is made of 10 GPS reference receivers, in red on this image:

(Source).
These stations are surveyed with great care and by multiple means very-long-baseline interferometry, satellite laser ranging, DORIS (and GNSS, after the frame initialization).
The second order network, the one used by everybody, is made of satellites, associated to the reference stations this way:

Satellites are launched and satellite tracking stations (black starts above), which positions are determined with respect to the reference frame, start tracking their orbits.

Each orbit is measured to determine the orbital elements describing the satellite timing and motion. As the orbital elements are measured using the tracking stations coordinates, the orbital elements are derived from the first order network of the red stations.

The orbital elements are uploaded by satellite control stations to the satellites. Each satellite continuously broadcasts its orbital elements and the current (atomic) time. This broadcast is technically equivalent to broadcasting the current XYZ coordinates of the satellite in the GPS frame. This also means these coordinates are fixed to the mean velocity of the tectonic plate.

A user with a GPS receiver passively receives at least four satellites. From the orbital elements and the atomic times they broadcast it determines the satellites XYZ coordinates, and from them, by multilateration, its own XYZ position in the GPS frame.
Displaying latitude, longitude and altitude values is a matter of coordinates transformation as seen above. As the GPS receiver is unlikely to be or to remain at the same velocity than the GPS frame, with time the coordinates it computes drift.
GPS frame realignment on the current ITRF
The mean tectonic drift is subject to permanent study in the context of the ITRS, the international terrestrial reference system, another ECEF coordinate system. Initially the GPS frame is aligned on the latest realization of the ITRS: The IRTF (F for frame). While the ITRS follows its own path with numerous GPS stations recording the drift of all plates, the WGS84/GPS frame stands on only 10 reference stations, indeed distributed on different plates, but the plates are subject to deformation. At some point in time, the ITRF and the WGS84 frames are de-aligned and it is desirable to re-align the WGS84 frame.
The realignement consists in updating the XYZ coordinates of the 10 reference stations. This change triggers in cascade, via the tracking stations and the satellites, a change of all GPS receiver coordinates.
The latest change, WGS84 (G2296), occurred in January 2024. The difference was only a few centimeters. The new coordinates of the stations:

(Source).
Since the GPS exists, its frame has been updated several times:

(Source).
The process is somehow similar to leap seconds and years used to realign UTC on actual solar time.
The first update (G730) led to a mean position change in the order of the meter, by far the largest change. It denoted the improvement in the accuracy of the reference stations coordinates.
From the epoch to the current velocities
While the frame is updated at intervals, it's still possible to get a better position than the one derived from the latest update. The solution is to know the current velocities of the reference stations, and to compute the displacements since the last update time (which is called the epoch of the frame). In the previous table for epoch 2024, velocities are found in the last columns.
Coordinates means nothing without a coordinate system
For a given latitude and longitude, unless you know which coordinate reference system (CRS) was used, e.g. NAD83 or WGS84, you can't say which place it indicates (errors of 100m or more are possible). The same coordinates, when used in three different coordinate systems points to distant locations:

(Source: Datums and Map Projections, Iliffe, Lott)
Knowing the CRS is not enough for certain uses. The CRS is the mathematical model, but coordinates are measured using the datum, realized at a given epoch. Different realizations leads to different coordinates, albeit the difference is not as important as between different systems.

Conceptually, yes they change over time with respect to locations on the earth.
Older mapping used a global model that assumed a static coordinate system, tied to the globe in one place (prime meridian).  But over the entire globe, continents have relative motion of centimeters per year.  It doesn't take too many years for some places to have enough motion for that to matter.  There have been construction problems due to ignoring this drift.
Australia is moving at something like 7cm/year.   Points mapped in the '90s might be a couple of meters away from where a current mapping might place them.
In the future, many places will start using reference frames tied to a specific tectonic plate and calculations will map that to a global lat/long for a specific date.

You are confusing the coordinates given by the GPS with the physical coordinates of a point. The physical coordinates will never change unless the earth moves, as in an earthquake, for example.
The GPS coordinates always have a margin of error, which the GPS itself will tell you. The margin of error will be within around 5 to 60 feet (higher with basic GPS, lower with additional info like WAAS). The margin of error can be affected by:

Satellite geometry
Signal blockage
Atmospheric conditions
Receiver design features/quality
Clear view of the sky
Obstacles like buildings or trees

While this is a good factual answer, I don't believe that it actually answers the OP's question about whether the GPS coordinates for a fixed point in earth ever change.

@Juan I understand the physical/geographic coordinates and GPS coordinates are different (as they're based 2 different model earths), but I'm talking about the GPS database. Are you saying that positions of stationary points (a WPT or APT) are also determined through satellites or are they pin-pointed on the GPS model on paper (not literally)? If the coordinates are calculated, not triangulated, then they shouldn't change unless for changes in the earth's shape - as I understand.

@PapaMike99 Not different because of any model, it's because one is based on surveying and the other by approximation of calculation. There is no "GPS database". There is no pinpoint of GPS models on paper. There are satellites and their info is used to calculate where you are, with a margin of error. Triangulation is calculation.

@JuanJimenez By databse I meant the database of our GPS navigation system in the aircraft. It has a database of airport, waypoints and procedures that need to be updated in order for that aircaft to legally use that GPS system for IFR navigation.

@PapaMike99 The coordinates of points in the GPS database are based on surveys of the land and use of highly previse advanced GPS receivers. The more advanced the receiver on the aircraft the more accurate it will be. The current top-of-the-line accuracy tech on civilian aircraft is WAAS. It will generate correction data for receivers equipped to get that info and correct to very small tolerances, but only if there is a nearbly operable WAAS station.

"The physical coordinates will never change unless the earth moves, as in an earthquake", it moves also by continental drift. In Australia, coordinates change by 7cm per year, when you build a bridge in 2 years it counts.

"The current top-of-the-line accuracy tech on civilian aircraft is WAAS", SBAS are available on all smartphones and GoPro, WAAS in the US, EGNOS in Europe, GAGAN in India, etc. The more advanced differential GNSS are ground-based augmentation systems used to land.

@mins Continental drift = Earth moves.

Let me give an attempt at this one.
So you have it slightly backward... "once the GPS coordinates of a point in space have been determined (say a GPS waypoint)." There are no GPS waypoints. There are RNAV waypoints defined by WGS84 coordinates. The coordinate system logically comes first. A location's lat/long is not based on GPS. Rather, GPS uses the same coordinate system.
Do coordinates change "due to correction of errors in pin-pointing/triangulating the position?" Technically, WGS84 does get updated. That's part of the Office of Geodesy at the National Geospatial-Intelligence Agency. https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84
For aviation purposes, this is far more precise than ever needed. In fact, in the US procedures designed by the FAA were based on NAD83 (horizontal datum) and NAVD88 (vertical datum). Since GPS was developed by the DoD, it was always based on WGS84. Likewise, your navigation database is based on WGS84. So consider this... procedures were designed based on a slightly different coordinate system and that is still considered "good enough." Note the FAA says this in the TPP legend:

Now that Performance Based Navigation has become widespread, any RNAV procedure with a navigation specification (NavSpec) is based on WGS84. So the procedure design, the aircraft's navigation database, and the GPS receiver are on the same reference system.


text:
Is airspace more crowded on days following cancellations or a large number of delays?
I am looking at some data form the BTS and trying to understand some spikes in month to month Volume delays. From my understanding a Volume delay is due to the volume of airplanes, causing the ATC to manage more take offs and landings and therefore slowing down the whole process.
My problem is that for volume delays bts only provides monthly aggregates. So I have data with a spike for Volume but the number of flights on that same month is normal or sometimes less than average. So I am assuming that something is happening at the daily level that is completely lost in the aggregation.
This all boils down to my question. If we where to quantify the capacity of the airspace around say ORD and call it X and on average the airspace is occupied with N planes, such that N < X and airspace is operating at N/X capacity.
On days following mass delays or large number of cancellations, does the amount of planes in the airspace increase to alleviate the pressure of passengers who are behind schedule? or does the load factor simply increase?
For examples say that on average airspace at ORD operates at 75% capacity, then one day you have some event that causes a lot of delays and cancellations. Do the following days operate at say 90% airspace capacity to help relive that congestion? or do they still operate the same number of planes but those planes are simply almost guaranteed to be full.
All summed up, would a spike in delays for some reason other than plane volume result in a spike in volume delay in the following days as they deal with the extra passengers?
Sorry if this question is worded strange, I had a hard time putting it down in writing. If its unclear let me know and I'll try to clarify.

It seems more related to air travel than aviation. Doesn't it boil down to "Is there more passengers flying after a lot of flight cancellations -- If so, does than mean more flights or more passengers per flight?"

Thanks that is a much simpler way of working it and I didnt realize air travel was a thing. I will post it there

@mins Seems perfectly on-topic here to me: it's a question about how the airlines manage flights, not a question seeking advice from a passenger's perspective.

I would say generally no, because there are only so many landing slots available at busy airports and airlines frequently substitute larger aircraft to clear up a passenger backlog.

Had not thought of that. So a typical flight scheduled to be flown with a certain plane might get switched to a larger plane with more seats?
In general would these planes require more spacing for take off and landing perhaps solving my mystery of increased volume delay with no increase in flight numbers?

Yes, essentially. Also the airline will regularly cancel domestic/short haul flights. Remember that there are only a fixed number of aircraft and airlines re already pretty good at utilising them efficiently - they don't just have a bunch of spares lying around most of the time.


text:
What advantages and disadvantages do tri planes have?
A triplane, mainly used in WW1 on the german side, was a biplane with 3 wings.
What were the advantages to having more wings?
And, why don't countries use them today?

Really very similar to the characteristics of biplanes.

but, if the charictaristics are so simillar, why add another wing, what advantage does it gain

It gains stronger characteristics.

Narrower wing chords versus a biplane of similar span and area.
More efficient and increased lift
Potentially faster rate of climb, tighter turning radius
Just to name a few.  You're essentially increasing the surface area without increasing the wingspan

Increased drag, probably increased weight as well.

Drag is dependent on velocity, triplanes were common when aircraft were slow and also needed slow stall speeds. When planes got faster they became obsolete due to the drag. (And improvements in wing support structures.)

@VilleNiemi, induced drag is inversely proportional to velocity and biplanes (and triplanes) have higher induced drag as well!

@JanHudec True, but IMHO higher induced drag is acceptable price to pay if you need low stall speed with limited wing span. Monoplanes operating from bad runways (or small bodies of water) still have to do the same trade-off, right?

@VilleNiemi, no, they don't. Bad runways don't mean your wing span would be particularly limited. In fact you want long span to get most of ground effect and you want to utilize ground effect for soft-field take-off (soft/rough-field technique is to unstick as soon as possible and accelerate in ground effect). And long span gives you lower induced drag and lower best glide speed (as the form drag then grows faster).

The accepted answer is wrong.
Triplanes have all the disadvantages of biplanes, only more so. But they share their advantages as well, and the main reason to build them in WW I was roll maneuverability:

The reduced wingspan reduced roll inertia, which helps to accelerate quickly into a high roll rate. Note that roll authority changes linearly with span (if the ailerons are scaled with the span), but inertia will change with span squared.
The reduced wingspan reduced  roll damping, so the achievable maximum roll rate is higher. The maximum roll rate is reached when the aileron-commanded rolling moment equals roll damping, and roll damping is proportional to span squared.

When the Sopwith Triplane became operational early in 1917, German pilots felt at a disadvantage and Reinhold Platz at Fokker created the famous Dr.I. The next generation were biplanes again, however, and the latest Fokker creation of WW I was actually a monoplane. The high climb rate of the Triplane was caused by its low wing loading and high power-to-weight ratio and more due to the lightweight construction and the advances in engines than the triplane layout.

What were the advantages to having more wings?

Adding a second wing creates a lightweight, stiff box girder. As for why people added even more wings, see this excellent answer.

And, why don't countries use them today?

Because countries don't use airplanes, pilots do.